The timer devices based on microprocessors or microcontrollers are used to control a huge number of electronic and electromechanical devices in a wide range of environmental and temperature conditions, using different power supply methods, from a very stable power supply until batteries.
The main problem to solve for the development of low cost battery powered devices, including fragrance, soap and insecticide dispensers with a timer device comprising one control unit is the consumption control.
A typical method used is to place a control unit in sleeping mode when it is not used, and periodically in an awakening mode in order to allow it to check for some scheduled activities.
The sleep mode reduces the activity of the control unit and its related consumptions near zero. This awakening mode can be accomplished using a particular timer present inside the control unit, and if it is not cleared before it expires, resets the control unit.
However, in these timer devices there are two problems that reduce the timing precision: the voltage and temperature variations affect the accuracy of the internal timers of the control unit, with a consequently variation of the timing generated by them, and the timer usually used is less accurate than other timers.
Since the timing generation is one of the keys of any control system, the accuracy used to accomplish them is essential for a correct operation of the timer device.
Alternative solutions, useful for low cost devices and able to produce an adequately timing require a circuitry external to the control unit. This circuitry increases the cost and complexity of the device, and reduces the number of the available ports on the control unit, normally reduced in the low cost control units.
Therefore, it is evident the need of a timer device and method that permits an accurate operation, even with changes of temperature and voltage and with a reduced cost.